We are requesting funds to purchase a new Gammacell-40 (GC40) animal irradiator from Nordion. The GC40 is a 137Cs irradiator with a central dose rate of about 110 rad/min, a chamber that holds 20 mice, a quiet continuous air supply, an independent backup timer, a backup battery power source and redundant systems for monitoring the irradiation parameters and position of sources. The GC40 also has security features, including operator identification and access codes as well as a physical key that controls the operation of the touchpad. This instrument will replace our old GC40 animal irradiator, which is 20 years old and no longer fully supported by the manufacturer. In fact, parts are no longer made for our GC40 and any repairs require parts to be scavenged from retired instruments (if available) or built from scratch. Thus, it is clear that the useful life of this instrument is near the end and that it should be replaced. Since the animal irradiator is an important and essential part of numerous research programs at the Institute, the replacement of the animal irradiator is now one of the Institute's highest priorities. The requested instrument has several advantages over the old instrument. First, the requested instrument has a continuous and quiet air supply for the irradiation chamber, rather than a noisy air compressor that frightens the mice and causes them to become very agitated. Second, the requested instrument has an electronic timer as well as a backup timer, rather than a temperamental mechanical timer that often fails during irradiation. Third, there is a battery backup on the requested instrument, but not the old one, that can run the entire instrument if the power fails. Fourth, while the old instrument only requires a key to operate, the new instrument requires a key as well as an electronic username and password, providing additional security and allowing use to be monitored. Finally, since the requested instrument is currently in production by Nordion, we will be able to get a service contract, and if something does go wrong, we will be able to obtain replacement parts. Thus, the main advantages of the new instrument over the old one are that the new instrument provides reliability, security, ease of record-keeping and up-to-date parts and service. [unreadable] [unreadable] [unreadable]